1. Field of the Invention
The present invention is generally directed to a surgical treatment for ocular pathology, and relates more particularly to a device and method for generating ultrasound onto at least one annular segment of the trabecular meshwork of an eye affected by glaucoma
2. Description of Related Art
In the field of ophthalmologic diseases, one of the main surgical act that is practiced is cataract surgery.
Cataracts cause the lens of an eye to become clouded, which interferes with proper transmission and focusing of light on the retina.
A common practice to alleviate this condition is by surgically removing the cataractic lens and replacing it with an artificial intraocular lens.
Phacoemulsification enables the removal of a cataractic lens through a small incision, for example between about 2.5 to about 4 mm.
In this procedure, a needle is inserted through the incision into the capsular bag of the crystalline lens and the needle is ultrasonically vibrated to mechanically emulsify the lens nucleus.
Once fragmented, or emulsified, the lens material is aspirated through a lumen through the phacoemulsification needle.
While emulsifying the lens and aspirating lens fragments, a simultaneous flow of irrigation fluid into the lens capsule is provided around the needle through an annulus established by a sleeve concentrically disposed over the needle.
This flow of liquid into the eye is necessary to prevent collapse of the anterior chamber of the eye during aspiration. In addition, the irrigation fluid cools the needle in order to prevent any thermal damage of the corneal or scleral tissue.
Phacoemulsification machines are very popular in the field of ocular medicine, and many surgeons have a phacoemulsificator for practicing cataract surgery.
It has to be noticed that the patients having a cataract often have a glaucoma. This is mainly due to the fact that both cataract and glaucoma affects most frequently aged patients.
It is well known that glaucoma is a significant public health problem, between 1 to 2% of population being suffering from this pathology, because glaucoma is a major cause of blindness.
The World health organisation considers glaucoma as the third cause of blindness in the world, responsible of 15% of declared blindness occurrences, with an incidence of 2.4 millions persons per year.
The evolution of glaucoma is slow. Glaucoma is an insidious health disease because at the first stage glaucoma is asymptomatic; the patient does not feel any pain or any visual problem. When the first visual troubles appear, lesions are commonly already large and despite irreversible.
The blindness that results from glaucoma involves both central and peripheral vision and has a major impact on an individual's ability to lead an independent life.
Glaucoma is an optic neuropathy, i.e. a disorder of the optic nerve, which usually occurs in the setting of an elevated intraocular pressure. The pressure within the eye increases and this is associated with changes in the appearance and function of the optic nerve. If the pressure remains high enough for a long period of time, total vision loss occurs. High pressure develops in an eye because of an internal fluid imbalance.
The eye is a hollow structure that contains a clear fluid called “aqueous humor.” Aqueous humor is formed in the posterior chamber of the eye by the ciliary body. The fluid, which is made at a fairly constant rate, then passes around the lens, through the pupillary opening in the iris and into the anterior chamber of the eye. Once in the anterior chamber, the fluid drains out of the eye through two different routes. In the “uveoscleral” route, the fluid percolates between muscle fibers of the ciliary body. This route accounts for approximately ten percent of the aqueous outflow in humans. The primary pathway for aqueous outflow in humans is through the “canalicular” route that involves the trabecular meshwork and Schlemm's canal.
With the increased pressure in the eye, the aqueous fluid builds up because it cannot exit fast enough. As the fluid builds up, the intraocular pressure (IOP) within the eye increases. The increased IOP compresses the axons in the optic nerve and also may compromise the vascular supply to the optic nerve. The optic nerve carries vision from the eye to the brain. Some optic nerves seem more susceptible to abnormally elevated IOP than other eyes.
One approach to treat glaucoma consist in trying to improve aqueous humor drainage.
The most practiced surgeries intended to improve the aqueous humor drainage are: canaloplasty, laser trabeculoplasty, laser peripheral iridotomy (in case of angle closure glaucoma), trabeculectomy, deep non perforating sclerectomy and glaucoma drainage implants.
Canaloplasty is an advanced, nonpenetrating procedure designed to enhance and restore the eye's natural drainage system to provide sustained reduction of IOP. Canaloplasty utilizes breakthrough micro catheter technology in a simple and minimally invasive procedure. To perform a canaloplasty, a doctor will create a tiny incision to gain access to a canal in the eye. A micro catheter will circumnavigate the canal around the iris, enlarging the main drainage channel and its smaller collector channels through the injection of a sterile, gel-like material. The catheter is then removed and a suture is placed within the canal and tightened. By opening the canal, the pressure inside the eye will be relieved.
Laser trabeculoplasty may be used to treat open angle glaucoma. A laser spot is aimed at the trabecular meshwork to stimulate opening of the mesh to allow more outflow of aqueous fluid. Usually, half of the angle is treated at a time.
There are two types of laser trabeculoplasty:                Argon laser trabeculoplasty (ALT) uses a laser to open up the drainage angle of the eye.        Selective laser trabeculoplasty (SLT) uses a lower-level laser to obtain the same result.        
Laser peripheral iridotomy may be used in patients susceptible to or affected by angle closure glaucoma. During laser iridotomy, laser energy is used to make a small full-thickness opening in the iris. This opening equalizes the pressure between the front and back of the iris, causing the iris to move backward.
The most common conventional surgery performed for glaucoma is the trabeculectomy. Here, a partial thickness flap is made in the scleral wall of the eye, and a window opening made under the flap to remove a portion of the trabecular meshwork. The scleral flap is then sutured loosely back in place. This allows fluid to flow out of the eye through this opening, resulting in lowered intraocular pressure and the formation of a bleb or fluid bubble on the surface of the eye under the conjunctiva.
Trabeculectomy is associated with many problems. Fibroblasts that are present in the episclera proliferate and migrate and can scar down the scleral flap. Failure from scarring may occur, particularly in children and young adults. Of eyes that have an initially successful trabeculectomy, eighty percent will fail from scarring within three to five years after surgery. To minimize fibrosis, surgeons now are applying antifibrotic agents such as mitomycin C (MMC) and 5-fluorouracil (5-FU) to the scleral flap at the time of surgery. The use of these agents has increased the success rate of trabeculectomy but also has increased the prevalence of hypotony. Hypotony is a problem that develops when aqueous flows out of the eye too fast. The eye pressure drops too low (usually less than 6.0 mmHg); the structure of the eye collapses and vision decreases. Antimetabolites directly applied on the surgical site can be used in order to improve the surgical prognosis, especially in high risk of failure (black patients, juvenile glaucoma . . . ).
Trabeculectomy creates a pathway for aqueous fluid to escape to the surface of the eye. At the same time, it creates a pathway for bacteria that normally live on the surface of the eye and eyelids to get into the eye. If this happens, an internal eye infection can occur called endophthalmitis. Endophthalmitis often leads to permanent and profound visual loss. Endophthalmitis can occur anytime after trabeculectomy. Another factor that contributes to infection is the placement of a bleb. Eyes that have trabeculectomy performed inferiorly have about five times the risk of eye infection than eyes that have a superior bleb. Therefore, initial trabeculectomy is performed superiorly under the eyelid, in either the nasal or temporal quadrant.
In addition to scarring, hypotony and infection, there are other complications of trabeculectomy. The bleb can tear and lead to profound hypotony. The bleb can be irritating and can disrupt the normal tear film, leading to blurred vision. Patients with blebs generally cannot wear contact lenses. All of the complications from trabeculectomy stem from the fact that fluid is being diverted from inside the eye to the external surface of the eye.
More recently a new surgical technique has been described, called Non-perforating deep sclerectomy ab externo. This technique allows avoiding to open the anterior chamber of the eye and consequently reduces the risk of postoperative complications. The major limitation of this technique is that it is a very difficult surgical technique and only a few surgeons are able to perform it successfully.
When trabeculectomy or sclerectomy doesn't successfully lower the eye pressure, the next surgical step often is an aqueous shunt device. There are several different glaucoma drainage implants. These include the original Molteno implant, the Baerveldt tube shunt, or the valved implants, such as the Ahmed glaucoma valve implant or the ExPress Mini Shunt and the later generation pressure ridge Molteno implants. These are indicated for glaucoma patients not responding to maximal medical therapy, with previous failed guarded filtering surgery (trabeculectomy). The flow tube is inserted into the anterior chamber of the eye and the plate is implanted underneath the conjunctiva to allow flow of aqueous fluid out of the eye into a chamber called a bleb.
The prior art includes a number of such aqueous shunt devices, such as U.S. Pat. No. 4,936,825, U.S. Pat. No. 5,127,901, U.S. Pat. No. 5,180,362, U.S. Pat. No. 5,433,701, U.S. Pat. No. 4,634,418, U.S. Pat. No. 4,787,885, U.S. Pat. No. 4,946,436, U.S. 20040015140A1 and U.S. Pat. No. 5,360,399.
Many complications are associated with aqueous shunt devices. A thickened wall of scar tissue that develops around the plastic plate offers some resistance to outflow and in many eyes limits the reduction in eye pressure. In some eyes, hypotony develops because the flow through the tube is not restricted. The surgery involves operating in the posterior orbit and many patients develop an eye muscle imbalance and double vision post-operatively. Moreover, because they are open to the surface of the eye, a pathway is created for bacteria to get into the eye and endophthalmitis can potentially occur.